1. Field of the Invention
This invention relates to automatic focus adjusting devices for still cameras, cine cameras and video cameras, and more particularly to automatic focus adjusting devices of the hybrid type having both a range finder of the active type in which a supersonic wave or an infrared light beam is projected onto an object to be photographed and its reflection is received to measure the object distance and another range finder of the passive type in which light coming from the object is received to measure the object distance.
2. Description of the Prior Art
A range finder of the active type is able to respond to objects of low brightness. Additionally, because the SN ratio of its signal becomes higher at shorter object distances, where the depth of field is shallow, the active type range finder generally has a high degree of accuracy. There are very few objects whose distances are impossible to measure with an active type range finder. However, there are limitations in the ability of active range finders to measure objects at far away distances for objects of law reflectivity and because the projected energy of an active range finder cannot be increased as much as desired. Additionally, the amount of electrical energy consumed is large.
Conversely, the passive type range finder is not limited by object distance or object reflectivity and consumes only a small amount of electrical power. However, it is almost impossible for the passive range finder to measure the distance to dim objects. Even where possible, the measurement takes a long time, e.g., half a second. Accordingly, there is a response gap in measuring distance, especially for moving objects. Moreover, the system becomes complicated because image processing of the object is also carried out. Finally, because of low contrast patterns, the passive range finder encounters a larger number of situations than the active range finder where it is impossible to measure object distance.